Wire the knowledge file adapter and a runtime path selector

main constructs the FileSource (default via ANTIDRIFT_KNOWLEDGE_FILE)
and injects it. Adds POST /knowledge/path to repoint the profile file at
runtime, and web tests asserting the planning payload carries the
knowledge object (status + path, never the text) and that path selection
reloads.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/web.go

@@ -58,6 +58,7 @@ func (s *Server) Router() *gin.Engine {
 	r.POST("/end", s.handleEnd)
 	r.POST("/refocus", s.handleRefocus)
 	r.POST("/ontask", s.handleOnTask)
+	r.POST("/knowledge/path", s.handleKnowledgePath)
 	return r
 }
 
@@ -124,6 +125,24 @@ func (s *Server) handleCommitment(c *gin.Context) {
 	s.respond(c, err)
 }
 
+type knowledgePathRequest struct {
+	Path string `json:"path"`
+}
+
+// handleKnowledgePath repoints the profile file at runtime (session-only). It
+// mutates config, not commitment state, so it never returns a transition error;
+// it just sets the path, re-loads, and broadcasts the refreshed state.
+func (s *Server) handleKnowledgePath(c *gin.Context) {
+	var req knowledgePathRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid json"})
+		return
+	}
+	s.ctrl.SetKnowledgePath(req.Path)
+	s.broadcast()
+	c.Data(http.StatusOK, "application/json", []byte(s.stateJSON()))
+}
+
 func (s *Server) handleComplete(c *gin.Context) {
 	s.cancelExpiry()
 	s.respond(c, s.ctrl.Complete())